The invention relates to a burner for the mixing and combustion of at least two combustion media.
In the case of such burners use can more particularly be made of combustion air and a poor or lean gas as the combustible gas. The burner comprises several burner nozzles, in each case a tube, which for the supply of a combustion medium extends to a combustion chamber and an inflow device for the other combustion medium can be provided at the combustion chamber-side end of the tube.
Such a burner is known from U.S. Pat. No. 5,267,850, which describes a burner system and a combustion process for high temperature applications. At one burner nozzle of the burner, a central high speed fuel flow is produced, which is annularly surrounded by a low speed flow.
Another burner used in connection with the hot gas producer is known from DE 42 08 951 C2. For the supply of one combustion medium the known burner has tubes, whose free ends are surrounded by the outlet nozzles for the inflow of a second combustion medium. This known arrangement leads to a very good complete combustion result in the case of a short burner flame. However, it is desirable to further improve the known burner with respect to the degree of complete combustion and the flame length.
The object of the invention is to provide a burner which, in the case of a short flame, also ensures a very complete combustion of combustion media even with very low calorific values.
According to the invention, this object is achieved by a burner nozzle provided with at least three mutually coaxially arranged tubes, namely an inner, core tube, an outer tube and at least one intermediate tube positioned between them. The tubes are radially spaced for forming annular clearance ducts, through which combustion media can be passed into the combustion chamber.
With this burner nozzle construction which, apart from the central core tube opening, has at least two annular clearance openings, the flame at the burner nozzle can be adjusted in virtually any desired manner. Thus, in accordance with the number of openings, it is possible to use more than two combustion media with different pressures. The at least three burner nozzle openings arranged concentrically to one another also ensure an intense mixing of the combustion media and consequently a particularly large combustion surface. This leads to a short flame and a very good degree of complete combustion. The stepped, axial arrangement of the tubes consequently ensures a mixing of the gases displaced as regards time and place in an optimum manner.
An advantage of the burner according to the invention is the possibility of operating it with so-called lean or poor gas, i.e. a combustible gas with a relatively low caloric value. With the hitherto known burners it was possible to achieve a spontaneous combustion with poor gases having a caloric value of at least approximately 2500 kJ/m.sup.3 (standard state). Tests have shown that with the burner according to the invention, even when using poor gases with a caloric value of approximately 1900 kJ/m.sup.3 (standard state), there is an independent combustion process. Thus, there is no need for additional burners with a high-grade combustible gas.
A particularly good combustion result is achieved through the tubes extending to a varying extent into the combustion chamber. Thus, the burner nozzle tubes have a stepped arrangement. The burner nozzle openings are mutually displaced in the axial direction of the tubes. This leads to a mixing of the different gaseous combustion media in place and time-displaced manner, which leads to a particularly good mixing of the media.
It is advantageous for the outer tube to extend further into the combustion chamber than the intermediate tube. Thus, the outer tube forms a lateral boundary of the burner nozzle, so that the influence of neighbouring burner nozzles on the mixing process is substantially avoided.
According to an advantageous embodiment, the core tube extends further into the combustion chamber than the intermediate tube. Thus, there is initially a mixing of the combustion media flowing out of the annular clearance ducts. Following mixing in the lateral areas of the burner nozzle, an additional turbulence and consequently a particularly large contact surface is obtained between the combustion media through the flow out of the core tube.
In order in this arrangement to ensure a good focussing or bundling of the flame of the individual burner nozzles, the outer tube extends further into the combustion chamber than the core tube.
According to a further development of the burner according to the invention a compartment is provided for each combustion medium and is line-connected to each burner nozzle. The individual, separate compartments in their turn have inlets, through which the combustion medium flows into the associated compartment, it being possible in simple manner to adjust in the compartments the particular pressure of the combustion medium.
This embodiment is further developed in that three compartments are provided, whereof the first compartment is connected to the core tube, the second compartment to the annular clearance duct formed by the core tube and the intermediate tube and the third compartment to the annular clearance duct formed by the intermediate tube and the outer tube. Thus, in this further development, a first combustion medium flows via the first compartment and the core tube into the combustion chamber. The second combustion medium flows via the second compartment and the associated annular clearance duct into the combustion chamber, whilst the third combustion medium is passed through the third compartment and the other annular clearance duct. As a result of this separate supply it is possible to achieve a good mixing in the case of three different combustion media.
According to an alternative embodiment, there are two compartments, whereof one is connected to the core tube and an annular clearance duct. The other compartment is then correspondingly connected with the one or more remaining annular clearance ducts. Thus, e.g. two combustion media can flow through several separate burner nozzle openings into the combustion chamber, which leads to a high and desired degree of turbulence.
It is also advantageous for certain applications for the burner nozzle to have four tubes. Then, besides the core tube opening, there are in all three annular clearance openings. Thus, in this embodiment, four combustion media can separately be supplied. When using less combustion media individual combustion media can be supplied via several burner nozzle openings in order to achieve a good mixing. If special applications justify the constructional expenditure, of course it is possible to provide burner nozzles with five or more tubes.
To improve the turbulence of the combustion media, it is advantageous to provide at the combustion chamber-side end of the burner nozzle whirl or swirl devices. The whirl devices can be substantially radially directed nozzles. A particularly simple and effective whirl device e.g. for the core tube, is provided by the construction of radially directed bores in the core tube wall, the free end of the core tube being closed or sealed by a plate.
In order to ensure a problem-free ignition, the burner according to the invention is so further developed that a starting burner is provided and around it are arranged the burner nozzles. The starting burner is supplied with separate combustion media, particularly a high-grade combustible gas. Following a certain start-up time, the starting burner can be switched off again.
A particular advantage of the invention is that one of the combustion media can be a sulphurous gas, particularly hydrogen sulphide. Up to now, such gases have had to be disposed of in an expensive manner, but can now be usefully thermally burned and recycled using the burner according to the invention.